My first thought was to build a .44x39mm thumper.
Unfortunately the case neck is going to be too thin for that.

Still playing with the ideas though and a 9×39 or 10×39 keep coming to mind.
Unfortunately the 9×39 will probably win out, the case would still have a vestigial shoulder and should still work through standard mags then.

Of course a 9mm Para version is a possibility as there’s a Uzi barrel sitting right there also.

Hmm. It’ll have to be a screw build because of the messed up holes, but for free….

I vote for the 9mm Para with the Uzi barrel. Some time down the road you may come up with a wild hair idea using that 430 blank!
Robin
((my newest carbine is a Hi-Point 45acp. Looking to break-in next weekend_))

Whirly,
I found this post on making rimless 444 Marlin using 6mm Remington brass. I didn’t chech the casehead sizing. But it might mach up well enough with the 762×39 to work.
I can’t see how a .243 can go up to a 44 if a 308 can’t but it’s not my project. But it does make me think cutting the top off a 30.06 to make 444 rimmless brass could posibly work. I’m telling you right up front I haven’t checked any case dimensions. But it is an interesting idea, an AK thumper in 444 would be a cool gun.

My vote is to chamber the .430 barrel for 44 Automag (edited). The case length for 44 mag is1.285. To make rimmless 44mag simply cutt a 7.62 x 39 case off at that length and run it through a 44mag sizing die.
The only thing needed is a reamer that will cut a chamber so the case can headspace on the case mouth. Reloading will be safe using 44mag data. As a bonus the cartridges will fit into standard AK magazines. 20, 30 or 40 rounds of 44 mag available for knocking over anything walking the planet. I think I want one!

Edit: I forgot about the Automag. It used 308 cases to make rimless 44 mag.

A build I really wanted to see is one a friend told me. Seems this guy had bunch of spare stuff laying around (yep, a basher. Takes stuff apart and then does Frankenstein builds) Made his own bullpup 17 cal. using necked down 45 shells. Travel a mile in nothing flat and straight.
Robin